Chk1p

Samples were loaded on 4–12% NuPAGE Bis-Tris Gel (Novex Life Technologies) and transferred to a polyvinylidene difluoride membrane (0.45 μm, Immobilon). Membranes were blocked with 5% BSA in PBS for 1 h at room temperature and incubated with primary antibodies diluted 1:1,000 in blocking buffer overnight at 4 °C. Primary antibodies were: H3K9me1 (Upstate, 07-450), H3K9me3 (Millipore, 07-442) mouse anti-H3 (Abcam, ab10799), γH2A.X (Millipore, 05-636), Chk1p (Cell Signaling, 2344), Chk1 (DCS-310 (ref. ^{98 (link)}), p53-S15p (Cell Signaling, 12571), p53 (Sigma-Aldrich, mouse monoclonal antibody, clone DO-1) and β-actin (Sigma-Aldrich, A5316). Membranes were washed in 0.1% Tween-20 in PBS on the following day, followed by incubation with secondary antibody coupled to near-infrared dyes CF 680/CF 770 (1:10,000). Antibodies were visualized using an Odyssey CLx infrared scanner (LiCor).

The antibodies used for immunoblotting were the ones against HA (1:2000, 11867423001, Roche), Myc (1:2000, clone 9E10, produced by IFOM facility), Chk1 (sc8408, Santa Cruz), Chk1-P (1:1000, 2341, Cell Signaling Technology), RPA (1:1000, A300-244A, Bethyl), Histone H3 (1:2000, ab1791, Abcam), Histone H3-P (1:1000, 06-570, Millipore), α-tubulin (1:3000, T5168, Sigma) and FLAG (1:2500, F3165, Sigma).
All uncropped blots in the main figures are shown in Supplementary Fig. 7.